Exams

Let the average of 8 men be x. Age of new man be N.
Total age of 8 men = 8x
⇒ x + 4 = ((8x – 30) + N)/8
⇒ 8x + 32 = 8x – 30 + N
⇒ N = 32 + 30
⇒ N = 62

Alfred Bernhard Nobel was a Swedish chemist, engineer, inventor, businessman, and philanthropist. Known for inventing Dynamite, Nobel also owned Bofors, which he had redirected from its previous role as primarily an iron and steel producer to a major manufacturer of cannon and other armaments.

There are 60 minutes in an hour.

In ¾ of an hour there are (60 × ¾) minutes = 45 minutes.

In ¾ of an hour there are (60 × 45) seconds = 2700 seconds.

Siren sounds for every 5 seconds.

In 2700 seconds = 2700/5 = 540 times.

The count start after the first sound, the Siren will sound 541 times in ¾ of an hour.